How will the excess use of machinery effect employment?

It's an interesting question. It can either increase or decrease employment. It depends whether you are talking about the short run or the long run.
For example, in the short run, machinery could increase employment. It can make workers more efficient because they can do more with the same amount of resources. The excess gains from the companies can allow them to employ more people moving forward.
However, some industries can suffer from complete automation all together. For example, self checkout at supermarkets. Similarly, self-driving cars can actually reduce employment because entire workforce can be replaced by machines.
Mark Zuckerberg made an interesting point around machine automation and universal income. Check it out if you're interested.